1. Field of the Invention
The present invention relates to a level shift circuit for shifting voltage levels from one to another in accordance with voltages needed by switches of a half-bridge configuration.
2. Description of the Related Art
A related level shift circuit is disclosed in Published Japanese Translation of PCT Application No. 2005-512444. This level shift circuit is for high- and low-side switches of a half-bridge configuration. In the half-bridge configuration, a high-side ground voltage at a midpoint of the high- and low-side switches greatly varies in the range of, for example, 0 V to 400 V with respect to a ground voltage in synchronization with ON/OFF operation of the high- and low-side switches. To drive the high-side switch in such circumstances, a high-side driver capable of applying a voltage higher than the high-side ground voltage is connected to a gate of the high-side switch.
The level shift circuit is connected to the high-side driver and includes first and second capacitors those are two passive devices. A rise edge of a pulse signal is supplied through a first driver to the first capacitor. The rise edge of the pulse signal is inverted through an inverter into a fall edge, which is supplied to the second capacitor. With the rise and fall edges, the first and second capacitors generate necessary currents.
Namely, the first and second capacitors generate temporary currents those are used to set/reset a latch at the timing appropriate for properly driving half-bridge drivers or similar circuits. The latch outputs a set/reset signal in response to which the high-side driver turns on/off the high-side switch.
If charging voltages of the first and second capacitors vary due to external factors other than set and reset signals, temporary currents pass through the first and second capacitors.